1. Field of the Invention
One embodiment of the present invention relates to a light-emitting element, a display module, a lighting module, a display device, a light-emitting device, an electronic device, and a lighting device in which the organic compound is used. Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, an imaging device, a method of driving any of them, and a method of manufacturing any of them.
2. Description of the Related Art
Light-emitting elements (organic EL elements) including organic compounds and utilizing electroluminescence (EL) have been put to more practical use. In the basic structure of such a light-emitting element, an organic compound layer containing a light-emitting substance (an EL layer) is provided between a pair of electrodes. By voltage application to this element, light emission from the light-emitting substance can be obtained.
Since such light-emitting elements are of self-light-emitting type, light-emitting elements have advantages over liquid crystal displays when used as pixels of a display in that visibility of pixels is high and backlight is not required. Thus, light-emitting elements are suitable as flat panel display elements. A display including such a light-emitting element is also highly advantageous in that it can be thin and lightweight. Besides, very high speed response is one of the features of such an element.
Since light-emitting layers of such light-emitting elements can be successively formed two-dimensionally, planar light emission can be achieved. This feature is difficult to realize with point light sources typified by incandescent lamps and LEDs or linear light sources typified by fluorescent lamps. Thus, light-emitting elements also have great potential as planar light sources, which can be applied to lighting devices and the like.
Displays or lighting devices including light-emitting elements can be suitably used for a variety of electronic devices as described above, and research and development of light-emitting elements have progressed for higher efficiency or longer lifetimes.
Patent Document 1 discloses a light-emitting element that achieves a long lifetime by including an electron-transport layer to which a substance having an electron-trapping property is added.